Drill bits used to drill wellbores through earth formations generally fall within one of two broad categories of bit structures. Drill bits in the first category are known as roller, or roller-cone, drill bits. Drill bits of this type usually include a bit body having at least one roller cone. Typically, roller cone drill bits are constructed as tri-cone bits, but di- and mono-cone drill bits are available. As the roller cone bit is rotated in contact with the formation, cutter elements mounted about the periphery of each roller cone roll over the bottom hole formation, scraping, crushing, and pulverizing the formation into small pieces that are carried to the surface with the returning annular fluid.
Drill bits of the second category are commonly known as fixed cutter or drag bits. Bits of this type usually include a bit body upon which a plurality of fixed cutting elements is disposed. Most commonly, the cutting elements disposed about the drag bit are manufactured of cylindrical or disk-shaped materials known as polycrystalline diamond compacts (PDCs). PDC cutters drill through the earth by scraping/shearing away the formation rather than pulverizing/crushing it. Fixed cutter and drag bits are often referred to as PDC or natural diamond (NDB) and impregnated bits. Like their roller-cone counterparts, PDC and in some cases NDB and impregnated bits also include an internal plenum through which fluid in the bore of the drill string is allowed to communicate with a plurality of fluid nozzles.
Drill bits of both types may have flow passages terminating in jet nozzles out of which fluids flow to clear drill cuttings from the bottom of the bore being drilled.